SUPPURA TION. 199 Martin is the formation of crystals in fresh cultures. Crystal-formation in cultures of other bacteria usually takes place in old, partially dried agar-agar cultures. The bacillus pyocyaneus, however, produces crystals in a few days upon fresh media. In my experience freshly iso- lated bacilli manifest this capability more markedly than those which have been for some time part of the labo- ratory stock of cultures, and subject to frequent trans- plantation.1 Upon potato a luxuriant greenish or brownish, smeary layer is produced. Milk is coagulated and peptonized. This bacillus is highly pathogenic for laboratory ani- mals. About i c.cm. of a fresh bouillon culture, if in- jected into the subcutaneous tissue of a guinea-pig or a *rabbit, causes a rapid edema, a suppurative inflammation, and death in a short time (twenty-four hours). Some- times the animal lives for a week or more, then dies. There is a marked hemorrhagic subcutaneous edema at the seat of inoculation. The bacilli can be found in the blood and in most of the tissues. When the dose is too small to prove fatal, suppuration occurs in many cases. When sterilized cultures are injected, the same results follow, a relatively larger quantity, of course, being re- quired. Intraperitoneal injections cause suppurative peritonitis. The organism has been found in the human being in the pus in cases of middle-ear disease (often in pure culture), panophthalmia, bronchopneumonia, inflammations of the nasal fossae, meningitis, etc. Escaping from such local lesions into the blood it sometimes causes nephritis. It may, however, be stated that ordinarily the bacillus is harmless for human beings, the above-mentioned ex- amples of pathogenic activity being marked exceptions. It is interesting to observe, in passing, that this path- ogeny can be set aside by the immunity which develops after a few inoculations with sterilized cultures. These 1 See Centralbl.f. Bakt., xxi., April 6, 1897, p. 473.